A Comparison of PWM Strategies for Inverter-Fed Induction Motors

Several sophisticated or "optimum" modulation strategies have been suggested for voltage source pulsewidth modulated (PWM) inverters for ac motor control. These modulation strategies may suppress specific low-order harmonics or minimize total harmonic content and have been successfully implemented in practical drive systems. The effectiveness of these PWM techniques in minimizing harmonic losses and reducing torque pulsations is investigated analytically, and their performance is compared with that of the usual sinusoidal or subharmonic PWM approach. The influence of skin effect on rotor 12R copper loss is taken into consideration, and harmonic core losses are compared. Peak current is also an. important factor in inverter design, and the various modulation strategies are again compared on this basis. Fourier analysis techniques are used in order to allow skin effect phenomena to be taken into consideration, and performance criteria are developed to allow comparisons of waveform quality in respect of harmonic copper and iron losses.